Crank No Start on the 6.7L Cummins Diesel Engine

[MikePhua]

The 6.7L Cummins and Its Electronic Fuel System
The 6.7L Cummins ISB engine, introduced in 2007, marked a major shift in medium-duty diesel technology. Designed for emissions compliance and electronic control, it replaced mechanical injection with a high-pressure common rail (HPCR) system. This system uses a CP3 or CP4 injection pump, a fuel rail, solenoid-controlled injectors, and a suite of sensors managed by the ECM (Engine Control Module). While powerful and efficient, the system is sensitive to fuel quality, electrical integrity, and sensor feedback.
Crank-no-start conditions on this engine are often electrical or fuel-related, and require a methodical approach to avoid unnecessary parts replacement.
Common Symptoms and Initial Observations
When the engine cranks but does not start, operators may notice:

• No fuel pressure at the rail
  
• No smoke from the exhaust during cranking
  
• No active fault codes on the dash
  
• Fuel lift pump audible but ineffective
  
• Rail pressure sensor reading zero or erratic
  
• Occasional sputter but no sustained ignition
  

These symptoms suggest that fuel is not reaching the injectors at sufficient pressure, or that the ECM is preventing injection due to missing sensor data.
Primary Causes of Crank-No-Start
Several root causes are frequently encountered:

• Failed fuel rail pressure sensor
  If the sensor reports zero pressure, the ECM will inhibit injection. Even if pressure exists, the ECM relies on sensor feedback to authorize firing.
  
• Faulty fuel control actuator (FCA)
  Mounted on the injection pump, the FCA regulates fuel volume. If stuck closed, it prevents rail pressurization. If stuck open, it floods the rail and causes hard starts.
  
• Air intrusion in fuel lines
  Leaks on the suction side of the lift pump allow air into the system, preventing priming and rail pressure buildup.
  
• Weak or failed lift pump
  The in-tank or frame-mounted lift pump may run but fail to deliver adequate volume. This starves the injection pump and causes dry cranking.
  
• Corroded or broken wiring to sensors
  The rail pressure sensor, FCA, and cam/crank sensors rely on clean signals. Rodent damage or vibration can break wires inside the loom.
  
• Failed camshaft or crankshaft position sensor
  Without synchronized timing input, the ECM will not initiate injection. These sensors are magnetic and can fail due to debris or heat.
  

A technician in Alberta once diagnosed a 6.7L Cummins that cranked endlessly with no smoke. After checking fuel delivery and replacing the FCA, the issue persisted. The culprit was a broken ground wire to the rail pressure sensor. Once repaired, the engine started immediately.
Diagnostic Strategy and Step-by-Step Testing
To isolate the fault:

• Scan the ECM for active and inactive fault codes
  
• Monitor live rail pressure during cranking—should exceed 5,000 psi to initiate injection
  
• Check voltage and ground at the rail pressure sensor
  
• Inspect the FCA for resistance and actuation
  
• Prime the fuel system manually and check for air bubbles
  
• Test cam and crank sensor signals with an oscilloscope or scan tool
  
• Verify lift pump output volume and pressure
  

If no codes are present, focus on live data. A rail pressure reading of zero during cranking almost always points to sensor failure or FCA malfunction.
Preventive Measures and Long-Term Reliability
To reduce future crank-no-start events:

• Replace fuel filters every 15,000 miles or 250 hours
  
• Use high-quality diesel with anti-gel additives in cold climates
  
• Inspect wiring harnesses annually for abrasion or corrosion
  
• Replace FCA and rail pressure sensor every 100,000 miles as preventive maintenance
  
• Avoid running the tank below ¼ full to prevent air ingestion
  
• Use dielectric grease on sensor connectors to prevent moisture intrusion
  

Some fleet managers install inline fuel pressure gauges and diagnostic tees to monitor system health in real time.
A Story from the Field
In 2022, a snowplow operator in Montana faced a crank-no-start on his 6.7L Cummins-powered truck during a blizzard. The lift pump ran, but no fuel reached the rail. After replacing the filters and FCA, the issue remained. A mobile technician discovered that the rail pressure sensor had failed internally, sending a flat zero signal to the ECM. Replacing the sensor restored full function, and the truck cleared roads within the hour.
Conclusion
Crank-no-start conditions on the 6.7L Cummins are often sensor-driven and require precise diagnostics. By focusing on rail pressure, FCA function, and timing inputs, technicians can resolve issues without guesswork. In electronically controlled diesels, fuel flow is only half the story—signal integrity is the other half. When both align, the engine roars to life and the work gets done.